1. Field of the Invention
The present invention relates to orthopedic surgery and in particular to devices and prosthesis for stabilizing and fixing the bones and joints of the body. Particularly, the present invention relates to a mono-axial, taper lock screw for securing a connecting rod to a vertebra, wherein the screw can be easily inserted into a vertebra and connected to a connecting rod that can be connected to other vertebrae not on the same plane and can provide a structural configuration that facilitates ease of insertion or removal of the screw as desired. More particularly, the present invention relates to a novel mono-axial, taper lock bone screw configured to provide a mono-axial rotational connection of the screw to a connecting rod so as to permit surgical manipulation of the spinal vertebrae alignment and connecting rod positioning and then being capable of securing the connecting rod firmly in the selected position relative to the screw and the underlying attached bone. Further, the present invention relates to a mono-axial, taper lock bone screw having a proximal flange that is easily accessible to facilitate the connection of a complementarily configured gripping tool for improved ease of locking and unlocking of the screw when desired.
2. Background of the Technology
It is a common surgical requirement to stabilize and fix bones and bone fragments in a particular spatial relationship to correct the location of skeletal components due to injury or disease. This can be accomplished by using a number of bone pins, anchors, or screws placed in bones across a discontinuity in the bone or bone fragments, such as a fracture, or adjacent vertebrae, or joint. They are connected by a rod to maintain a predetermined spatial location of the bones or bone fragments. In some cases the use of these devices may be permanently implanted in the subject. In other cases, the devices may be implanted only as a temporary means of stabilizing or fixing the bones or bone fragments, with subsequent removal when no longer needed. It is also common that device implants that were intended to be permanent may require subsequent procedures or revisions as the dynamics of the subject's condition warrant. For these reasons, it is desirable that an implanted device be provided, which can be easily locked and unlocked as desired by the surgeon.
Spinal fixation apparatuses are widely employed in surgical processes for correcting spinal injuries and diseases. These apparatuses commonly employ longitudinally linked rods secured to the bone, such as vertebrae, by spinal bone fixation fasteners such as pedicle screws, hooks and others.
Many conventional bone screws do not provide a connection to a connecting rod wherein the connecting rod can be easily connected to adjacent vertebrae, which are not aligned on the same plane. Further, conventional bone screws do not allow any flexibility for alignment of the connecting rod in cases where a degree of flexibility would be desirable, such as, for example in treatment of the spine for scoliosis. Some effort has been made to provide screws that can be implanted into bone on varying planes; however, even for devices that have attempted to address the issue of securing rods to differently aligned vertebrae, such screws are not easily locked and unlocked and do not provide a mono-axial degree of flexibility and spinal manipulation that would be desirable in the treatment of some spinal conditions, such as scoliosis.
To meet the problem of securely connecting adjacent vertebrae, not on a common plane and that permit a mono-axial degree of flexibility for the screw head, a requirement exists to provide a mono-axial, taper lock screw that can be easily inserted and easily removed from the vertebral bone as desired. It is also desirable that such a screw be configured so that it can be locked into position in relation to the bone and the connecting rod without the need to exert any additional torque to the device or force on the patient. Additionally, such a mono-axial screw that can be used without the need for an additional locking piece, such as a set screw or the need to thread a locking device into place is desired.
Conventional efforts to treat such conditions, as for example, scoliosis, include the use of rigid screw and connecting rod connections. Such conventional connections fail to provide any degree of flexibility during the surgical procedure during which the surgeon manipulates and positions the spinal vertebrae into a desired alignment prior to locking the connecting rods into a rigid connection to the bone screws. More recently, polyaxial bone screws have been introduced and have greatly increased the ease of introducing and locking a connecting rod when building a spinal construct. However, flexible connections, such as polyaxial bone screws, provide too great a range of motion in cases such as scoliosis, and therefore, it is important that the flexibility during the spinal column manipulation process be restricted to allow only mono-axial movement of the connecting rod relative to the bone screw. The surgeon's manipulation forces on the spinal column and the implanted system should be effective in properly positioning the spinal column. However, if a conventionally provided connecting rod and screw system fails to limit the movements of the screw head to a single plane the force of the surgeon's manipulations could instead result in the head of the screw pivoting or rotating to one side or the other relative to the longitudinal axis of the spinal screw. Similarly, in the case of a rigid bone screw, spinal manipulation is more easily accomplished but attachment of the connecting rod is more difficult. Only a mono-axial screw head that limits movement to a single plane can avoid the unwanted multi-axial movement of the screw head during manipulation of the spine while still providing ease of attachment of the connecting rod. Further, conventional screw heads fail to provide a screw head configuration that presents ease of locking and unlocking the rod to the screw.
Thus a need exists for a system of screws and connecting rods that, during the surgical manipulation of the spine, is capable of permitting flexibility of the connecting rod position relative to the inserted bone screw in one plane while restricting movement in all other planes, thus, allowing only selected movement of the screw head-connecting rod attachment prior to locking the system in place. A need also exists for such a mono-axial, taper lock screw that is capable of being locked easily when grasped by a complementary configured tool that can be used by an operator for locking and unlocking the rod and screw.